Deploy hosted relay to `wss://relay.annotate-js.workers.dev`

[kasunben]

Context

The relay code in relay/ (Cloudflare Worker + Durable Object) is complete and ready to deploy. Until it is live, Tier 1 signaling fails silently on every P2P connection and falls through to NOSTR, producing console warnings that are confusing for users and misrepresent the architecture.

This is a v1 blocker. Shipping v1 while the primary signaling tier is non-functional is not acceptable regardless of the NOSTR fallback working correctly.

What needs to happen

• Deploy relay/worker.js via wrangler using relay/wrangler.toml
• Verify sub-second peer discovery via the hosted relay in a two-browser test
• Confirm the three-tier fallback still works correctly: hosted relay → self-hosted relay → NOSTR
• Remove the "Heads up: hosted relay not yet deployed" warning from the README once live

Acceptance criteria

• wss://relay.annotate-js.workers.dev is live and accepting WebSocket connections
• P2P demo connects via Tier 1 without falling back to NOSTR under normal conditions
• Console warnings about relay failure no longer appear in standard P2P usage
• README updated to reflect relay is live